In some process chambers, for example in epitaxial deposition chambers for processing semiconductor substrates, heat sources providing radiant energy, such as halogen lamps, may be used to heat a target element in the chamber. In some cases, the target may be, for example, a susceptor for supporting a substrate. For a variety of reasons, it is often desirable to measure the temperature of the susceptor during processing. In some cases, measuring the temperature of a susceptor cannot be achieved with direct measurement devices such as thermocouples. The temperature can be sensed using remote temperature sensors capable of detecting thermal radiation, for example, pyrometers, to detect a signal emitted by the susceptor that is proportional to the temperature of the susceptor.
The inventors have observed that radiant energy from the heat source may be reflected from the susceptor and received by the temperature sensor in the form of noise, interfering with an accurate measurement of the temperature signal from the susceptor. The noise may decrease the signal to noise ratio and/or provide a signal with a wavelength detectable by the temperature sensor.
Accordingly, the inventors have provided methods and apparatus to improve the measurement of the temperature signal from the target.